In response to RFA-HL-08-012 members of the Stem/Progenitor Cell Program of the Fred Hutchinson Cancer Research Center/University of Washington consortium propose a multifaceted program to generate molecular profiles of functionally defined progenitor populations to instruct strategies for controlling cell fate decisions. Our goal is to use molecular interventions to generate lineage-specific cell therapies. Over 40 years of marrow transplantation have taught us that human hematopoiesis is supported by a population of multipotent hematopoietic stem cells that can maintain or reconstitute the various blood cell lineages throughout life. Despite advances in our understanding of lineage commitment, this has not translated into improved approaches for treating lineage specific cytopenias. The goal of our application is to further our understanding of lineage commitment while simultaneously using this knowledge to develop clinically applicable molecular interventions that will drive hematopoiesis toward desired lineages both in vitro and in vivo. Towards this goal we propose a multifaceted program with 5 projects. In Project 1 we will generate molecular profiles of functionally defined progenitors in three species;mouse, dog, and man. These three experimental models have complimentary strengths that allow for a comprehensive approach including a robust preclinical in vivo model that can predict clinical outcomes. The second project will use these purified populations to identify cDNAs, microRNAs, or shRNAs that can direct hematopoietic commitment toward desired lineages. A third project will test the proliferation and differentiation potential of distinct progenitor subsets in response to conditionally activated signaling molecules. These studies will use signaling molecule derivatives that can be activated in response to small molecule drugs called chemical inducers of dimerization (CIDs). The fourth project will combine the gain and loss of function strategies from project 2 with the derived signaling molecules from project 3 to generate cells that can be directed to a specific lineage and expanded. Finally the dog model will be used to test the application of these strategies for generating lineage specific progenitors both ex vivo and in vivo to direct hematopoietic reconstitution.